Resonant power transfer systems with protective algorithm

ABSTRACT

Systems for tuning a wireless power transfer system are provided, which may include any number of features. In one embodiment, a TET system includes a receive resonator is adapted to be implanted in a human patient and is configured to receive wireless power from a transmit resonator. The system can include a controller configured to identify if a foreign object is interfering with the transmission of power or generating an induced voltage in the receive resonator. The controller can also be configured to control the transmit resonator to phase match with the foreign object. Methods of use are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/676,699, filed on Jul. 27, 2012, titled “ResonantPower Transfer Systems with Protective Algorithm”.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD

This disclosure relates generally to methods and apparatus fortransmitting and receiving power wirelessly, and in various respects,mechanical circulatory support.

BACKGROUND

Powered devices need to have a mechanism to supply power to theoperative parts. Typically systems use a physical power cable totransfer energy over a distance. There has been a continuing need forsystems that can transmit power efficiently over a distance withoutphysical structures bridging the physical gap.

Systems and methods that supply power without electrical wiring aresometimes referred to as wireless energy transmission (WET). Wirelessenergy transmission greatly expands the types of applications forelectrically powered devices. One such example is the field ofimplantable medical devices. Implantable medical devices typicallyrequire an internal power source able to supply adequate power for thereasonable lifetime of the device or an electrical cable that traversesthe skin. Typically an internal power source (e.g. battery) is feasiblyfor only low power devices like sensors. Likewise, a transcutaneouspower cable significantly affects quality of life (QoL), infection risk,and product life, among many drawbacks.

More recently there has been an emphasis on systems that supply power toan implanted device without using transcutaneous wiring. This issometimes referred to as a Transcutaneous Energy Transfer System (TETS).Frequently energy transfer is accomplished using two magneticallycoupled coils set up like a transformer so power is transferredmagnetically across the skin. Conventional systems are relativelysensitive to variations in position and alignment of the coils. In orderto provide constant and adequate power, the two coils need to bephysically close together and well aligned.

A problem can occur when a TET system interacts with other TET systemsand/or materials with magnetic susceptibility. For example, there isrisk of interference with a TET system if the user gets into a car. Ametal object essentially changes the inductance and characteristics ofthe circuit. Another risk involves two users with TET systems gettingnear each other. These problems must be solved to ensure the safety ofusers with implanted TET systems.

SUMMARY OF THE DISCLOSURE

A method of protecting a wireless power transfer system from foreigninterference is provided, comprising the steps of transmitting wirelesspower from a transmit resonator to a receive resonator implanted in ahuman patient, identifying if a foreign object is interfering with thetransmission of power or generating an induced voltage in the receiveresonator, and if a foreign object is interfering with the transmissionof power, controlling the transmit resonator to phase match with theforeign object.

In some embodiments, the method further comprises indicating to thepatient whether the foreign object is interfering with transmission ofpower.

In one embodiment, the indentifying step further comprises halting thetransmission of power, then determining if the receive resonator picks aforeign wireless power signal.

In another embodiment, the identifying step further comprises detectinga return energy transmitted from the receive resonator to the transmitresonator, and comparing the return energy to an expected return energyvalue.

In some embodiments, the identifying step further comprises identifyingthat the foreign object is interfering with the transmission of power bydetecting a wireless power signal in the receive resonator inapproximately the same frequency band as an operating frequency of thewireless power transfer system.

A wireless power transfer system is also provided, comprising a transmitresonator configured to transmit wireless power a receive resonatoradapted to be implanted in a human patient and configured to receivewireless power from the transmit resonator, and a controller configuredto identify if a foreign object is interfering with the transmission ofpower or generating an induced voltage in the receive resonator, thecontroller configured to control the transmit resonator to phase matchwith the foreign object.

In some embodiments, the controller is a transmit controller connectedto the transmit resonator.

In another embodiment, the controller is a receive controller connectedto the receive resonator.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a basic wireless power transfer system.

FIG. 2 illustrates the flux generated by a pair of coils.

FIGS. 3A-3B illustrate the effect of coil alignment on the couplingcoefficient.

FIG. 4 illustrates on embodiment of a TET system.

FIG. 5 is a flowchart illustrating one method of utilizing a protectivealgorithm in a TET system.

DETAILED DESCRIPTION

In the description that follows, like components have been given thesame reference numerals, regardless of whether they are shown indifferent embodiments. To illustrate an embodiment(s) of the presentdisclosure in a clear and concise manner, the drawings may notnecessarily be to scale and certain features may be shown in somewhatschematic form. Features that are described and/or illustrated withrespect to one embodiment may be used in the same way or in a similarway in one or more other embodiments and/or in combination with orinstead of the features of the other embodiments.

Various aspects of the invention are similar to those described inInternational Patent Pub. No. WO2012045050; U.S. Pat. Nos. 8,140,168;7,865,245; 7,774,069; 7,711,433; 7,650,187; 7,571,007; 7,741,734;7,825,543; 6,591,139; 6,553,263; and 5,350,413; and U.S. Pub. Nos.2010/0308939; 2008/027293; and 2010/0102639, the entire contents ofwhich patents and applications are incorporated herein for all purposes.

Wireless Power Transmission System

Power may be transmitted wirelessly by magnetic induction. In variousembodiments, the transmitter and receiver are closely coupled.

In some cases “closely coupled” or “close coupling” refers to a systemthat requires the coils to be very near each other in order to operate.In some cases “loosely coupled” or “loose coupling” refers to a systemconfigured to operate when the coils have a significant spatial and/oraxial separation, and in some cases up to distance equal to or less thanthe diameter of the larger of the coils. In some cases, “looselycoupled” or “loose coupling” refers a system that is relativelyinsensitive to changes in physical separation and/or orientation of thereceiver and transmitter.

In various embodiments, the transmitter and receiver are non-resonantcoils. For example, a change in current in one coil induces a changingmagnetic field. The second coil within the magnetic field picks up themagnetic flux, which in turn induces a current in the second coil. Anexample of a closely coupled system with non-resonant coils is describedin International Pub. No. WO2000/074747, incorporated herein for allpurposes by reference. A conventional transformer is another example ofa closely coupled, non-resonant system. In various embodiments, thetransmitter and receiver are resonant coils. For example, one or both ofthe coils is connected to a tuning capacitor or other means forcontrolling the frequency in the respective coil. An example of closelycoupled system with resonant coils is described in International Pub.Nos. WO2001/037926; WO2012/087807; WO2012/087811; WO2012/087816;WO2012/087819; WO2010/030378; and WO2012/056365, and U.S. Pub. No.2003/0171792, incorporated herein for all purposes by reference.

In various embodiments, the transmitter and receiver are looselycoupled. For example, the transmitter can resonate to propagate magneticflux that is picked up by the receiver at relatively great distances. Insome cases energy can be transmitted over several meters. In a looselycoupled system power transfer may not necessarily depend on a criticaldistance. Rather, the system may be able to accommodate changes to thecoupling coefficient between the transmitter and receiver. An example ofa loosely coupled system is described in International Pub. No.WO2012/045050, incorporated herein for all purposes by reference.

Power may be transmitted wirelessly by radiating energy. In variousembodiments, the system comprises antennas. The antennas may be resonantor non-resonant. For example, non-resonant antennas may radiateelectromagnetic waves to create a field. The field can be near field orfar field. The field can be directional. Generally far field has greaterrange but a lower power transfer rate. An example of such a system forradiating energy with resonators is described in International Pub. No.WO2010/089354, incorporated herein for all purposes by reference. Anexample of such a non-resonant system is described in International Pub.No. WO2009/018271, incorporated herein for all purposes by reference.Instead of antenna, the system may comprise a high energy light sourcesuch as a laser. The system can be configured so photons carryelectromagnetic energy in a spatially restricted, direct, coherent pathfrom a transmission point to a receiving point. An example of such asystem is described in International Pub. No. WO2010/089354,incorporated herein for all purposes by reference.

Power may also be transmitted by taking advantage of the material ormedium through which the energy passes. For example, volume conductioninvolves transmitting electrical energy through tissue between atransmitting point and a receiving point. An example of such a system isdescribed in International Pub. No. WO2008/066941, incorporated hereinfor all purposes by reference.

Power may also be transferred using a capacitor charging technique. Thesystem can be resonant or non-resonant. Exemplars of capacitor chargingfor wireless energy transfer are described in International Pub. No.WO2012/056365, incorporated herein for all purposes by reference.

The system in accordance with various aspects of the invention will nowbe described in connection with a system for wireless energy transfer bymagnetic induction. The exemplary system utilizes resonant powertransfer. The system works by transmitting power between the twoinductively coupled coils. In contrast to a transformer, however, theexemplary coils are not coupled together closely. A transformergenerally requires the coils to be aligned and positioned directlyadjacent each other. The exemplary system accommodates looser couplingof the coils.

While described in terms of one receiver coil and one transmitter coil,one will appreciate from the description herein that the system may usetwo or more receiver coils and two or more transmitter coils. Forexample, the transmitter may be configured with two coils—a first coilto resonate flux and a second coil to excite the first coil. One willfurther appreciate from the description herein that usage of “resonator”and “coil” may be used somewhat interchangeably. In various respects,“resonator” refers to a coil and a capacitor connected together.

In accordance with various embodiments of this disclosure, the systemcomprises one or more transmitters configured to transmit powerwirelessly to one or more receivers. In various embodiments, the systemincludes a transmitter and more than one receiver in a multiplexedarrangement. A frequency generator may be electrically coupled to thetransmitter to drive the transmitter to transmit power at a particularfrequency or range of frequencies. The frequency generator can include avoltage controlled oscillator and one or more switchable arrays ofcapacitors, a voltage controlled oscillator and one or more varactors, aphase-locked-loop, a direct digital synthesizer, or combinationsthereof. The transmitter can be configured to transmit power at multiplefrequencies simultaneously. The frequency generator can include two ormore phase-locked-loops electrically coupled to a common referenceoscillator, two or more independent voltage controlled oscillators, orcombinations thereof. The transmitter can be arranged to simultaneouslydelivery power to multiple receivers at a common frequency.

In various embodiments, the transmitter is configured to transmit a lowpower signal at a particular frequency. The transmitter may transmit thelow power signal for a particular time and/or interval. In variousembodiments, the transmitter is configured to transmit a high powersignal wirelessly at a particular frequency. The transmitter maytransmit the high power signal for a particular time and/or interval.

In various embodiments, the receiver includes a frequency selectionmechanism electrically coupled to the receiver coil and arranged toallow the resonator to change a frequency or a range of frequencies thatthe receiver can receive. The frequency selection mechanism can includea switchable array of discrete capacitors, a variable capacitance, oneor more inductors electrically coupled to the receiving antenna,additional turns of a coil of the receiving antenna, or combinationsthereof.

In general, most of the flux from the transmitter coil does not reachthe receiver coil. The amount of flux generated by the transmitter coilthat reaches the receiver coil is described by “k” and referred to asthe “coupling coefficient.”

In various embodiments, the system is configured to maintain a value ofk in the range of between about 0.2 to about 0.01. In variousembodiments, the system is configured to maintain a value of k of atleast 0.01, at least 0.02, at least 0.03, at least 0.04, or at least0.05.

In various embodiments, the coils are physically separated. In variousembodiments, the separation is greater than a thickness of the receivercoil. In various embodiments, the separation distance is equal to orless than the diameter of the larger of the receiver and transmittercoil.

Because most of the flux does not reach the receiver, the transmittercoil must generate a much larger field than what is coupled to thereceiver. In various embodiments, this is accomplished by configuringthe transmitter with a large number of amp-turns in the coil.

Since only the flux coupled to the receiver gets coupled to a real load,most of the energy in the field is reactive. The current in the coil canbe sustained with a capacitor connected to the coil to create aresonator. The power source thus only needs to supply the energyabsorbed by the receiver. The resonant capacitor maintains the excessflux that is not coupled to the receiver.

In various embodiments, the impedance of the receiver is matched to thetransmitter. This allows efficient transfer of energy out of thereceiver. In this case the receiver coil may not need to have a resonantcapacitor.

Turning now to FIG. 1, a simplified circuit for wireless energytransmission is shown. The exemplary system shows a series connection,but the system can be connected as either series or parallel on eitherthe transmitter or receiver side.

The exemplary transmitter includes a coil Lx connected to a power sourceVs by a capacitor Cx. The exemplary receiver includes a coil Lyconnected to a load by a capacitor Cy. Capacitor Cx may be configured tomake Lx resonate at a desired frequency. Capacitance Cx of thetransmitter coil may be defined by its geometry. Inductors Lx and Ly areconnected by coupling coefficient k. Mxy is the mutual inductancebetween the two coils. The mutual inductance, Mxy, is related tocoupling coefficient, k.

Mxy=k√{square root over (Lx·Ly)}

In the exemplary system the power source Vs is in series with thetransmitter coil Lx so it may have to carry all the reactive current.This puts a larger burden on the current rating of the power source andany resistance in the source will add to losses.

The exemplary system includes a receiver configured to receive energywirelessly transmitted by the transmitter. The exemplary receiver isconnected to a load. The receiver and load may be connected electricallywith a controllable switch.

In various embodiments, the receiver includes a circuit elementconfigured to be connected or disconnected from the receiver coil by anelectronically controllable switch. The electrical coupling can includeboth a serial and parallel arrangement. The circuit element can includea resistor, capacitor, inductor, lengths of an antenna structure, orcombinations thereof. The system can be configured such that power istransmitted by the transmitter and can be received by the receiver inpredetermined time increments.

In various embodiments, the transmitter coil and/or the receiver coil isa substantially two-dimensional structure. In various embodiments, thetransmitter coil may be coupled to a transmitter impedance-matchingstructure. Similarly, the receiver coil may be coupled to a receiverimpedance-matching structure. Examples of suitable impedance-matchingstructures include, but are not limited to, a coil, a loop, atransformer, and/or any impedance-matching network. Animpedance-matching network may include inductors or capacitorsconfigured to connect a signal source to the resonator structure.

In various embodiments, the transmitter is controlled by a controller(not shown) and driving circuit. The controller and/or driving circuitmay include a directional coupler, a signal generator, and/or anamplifier. The controller may be configured to adjust the transmitterfrequency or amplifier gain to compensate for changes to the couplingbetween the receiver and transmitter.

In various embodiments, the transmitter coil is connected to animpedance-matched coil loop. The loop is connected to a power source andis configured to excite the transmitter coil. The first coil loop mayhave finite output impedance. A signal generator output may be amplifiedand fed to the transmitter coil. In use power is transferredmagnetically between the first coil loop and the main transmitter coil,which in turns transmits flux to the receiver. Energy received by thereceiver coil is delivered by Ohmic connection to the load.

One of the challenges to a practical circuit is how to get energy in andout of the resonators. Simply putting the power source and load inseries or parallel with the resonators is difficult because of thevoltage and current required. In various embodiments, the system isconfigured to achieve an approximate energy balance by analyzing thesystem characteristics, estimating voltages and currents involved, andcontrolling circuit elements to deliver the power needed by thereceiver.

In an exemplary embodiment, the system load power, P_(L), is assumed tobe 15 Watts and the operating frequency of the system, f, is 250 kHz.Then, for each cycle the load removes a certain amount of energy fromthe resonance:

$e_{L} = {\frac{P_{L}}{f} = {60\mspace{14mu} µ\; J\mspace{14mu} {Energy}\mspace{14mu} {the}\mspace{14mu} {load}\mspace{14mu} {removes}\mspace{14mu} {from}\mspace{14mu} {one}\mspace{14mu} {cycle}}}$$e_{L} = {\frac{P_{L}}{f} = {60\mspace{14mu} µ\; J\mspace{14mu} {Energy}\mspace{14mu} {the}\mspace{14mu} {load}\mspace{14mu} {removes}\mspace{14mu} {in}\mspace{14mu} {one}\mspace{14mu} {cycle}}}$

It has been found that the energy in the receiver resonance is typicallyseveral times larger than the energy removed by the load for operative,implantable medical devices. In various embodiments, the system assumesa ratio 7:1 for energy at the receiver versus the load removed. Underthis assumption, the instantaneous energy in the exemplary receiverresonance is 420 μJ.

The exemplary circuit was analyzed and the self inductance of thereceiver coil was found to be 60 uH. From the energy and the inductance,the voltage and current in the resonator could be calculated.

$e_{y} = {\frac{1}{2}{Li}^{2}}$$i_{y} = {\sqrt{\frac{2\; e_{y}}{L}} = {3.74\mspace{14mu} A\mspace{14mu} {peak}}}$v_(y) = ω L_(y)i_(y) = 352  V  peak

The voltage and current can be traded off against each other. Theinductor may couple the same amount of flux regardless of the number ofturns. The Amp-turns of the coil needs to stay the same in this example,so more turns means the current is reduced. The coil voltage, however,will need to increase. Likewise, the voltage can be reduced at theexpense of a higher current. The transmitter coil needs to have muchmore flux. The transmitter flux is related to the receiver flux by thecoupling coefficient. Accordingly, the energy in the field from thetransmitter coil is scaled by k.

$e_{x} = \frac{e_{y}}{k}$

Given that k is 0.05:

$e_{x} = {\frac{420\mspace{14mu} µ\; J}{0.05} = {8.4\mspace{14mu} {mJ}}}$

For the same circuit the self inductance of the transmitter coil was 146uH as mentioned above. This results in:

$i_{x} = {\sqrt{\frac{2\; e_{x}}{L}} = {10.7\mspace{14mu} A\mspace{14mu} {peak}}}$v_(x) = ω L_(x)i_(x) = 2460  V  peak

One can appreciate from this example, the competing factors and how tobalance voltage, current, and inductance to suit the circumstance andachieve the desired outcome. Like the receiver, the voltage and currentcan be traded off against each other. In this example, the voltages andcurrents in the system are relatively high. One can adjust the tuning tolower the voltage and/or current at the receiver if the load is lower.

Estimation of Coupling Coefficient and Mutual Inductance

As explained above, the coupling coefficient, k, may be useful for anumber of reasons. In one example, the coupling coefficient can be usedto understand the arrangement of the coils relative to each other sotuning adjustments can be made to ensure adequate performance. If thereceiver coil moves away from the transmitter coil, the mutualinductance will decrease, and ceteris paribus, less power will betransferred. In various embodiments, the system is configured to maketuning adjustments to compensate for the drop in coupling efficiency.

The exemplary system described above often has imperfect information.For various reasons as would be understood by one of skill in the art,the system does not collect data for all parameters. Moreover, becauseof the physical gap between coils and without an external means ofcommunications between the two resonators, the transmitter may haveinformation that the receiver does not have and vice versa. Theselimitations make it difficult to directly measure and derive thecoupling coefficient, k, in real time.

Described below are several principles for estimating the couplingcoefficient, k, for two coils of a given geometry. The approaches maymake use of techniques such as Biot-Savart calculations or finiteelement methods. Certain assumptions and generalizations, based on howthe coils interact in specific orientations, are made for the sake ofsimplicity of understanding. From an electric circuit point of view, allthe physical geometry permutations can generally lead to the couplingcoefficient.

If two coils are arranged so they are in the same plane, with one coilcircumscribing the other, then the coupling coefficient can be estimatedto be roughly proportional to the ratio of the area of the two coils.This assumes the flux generated by coil 1 is roughly uniform over thearea it encloses as shown in FIG. 2.

If the coils are out of alignment such that the coils are at a relativeangle, the coupling coefficient will decrease. The amount of thedecrease is estimated to be about equal to the cosine of the angle asshown in FIG. 3A. If the coils are orthogonal to each other such thattheta (0) is 90 degrees, the flux will not be received by the receiverand the coupling coefficient will be zero.

If the coils are arranged such that half the flux from one coil is inone direction and the other half is in the other direction, the fluxcancels out and the coupling coefficient is zero, as shown in FIG. 3B.

A final principle relies on symmetry of the coils. The couplingcoefficient and mutual inductance from one coil to the other is assumedto be the same regardless of which coil is being energized.

M _(xy) =M _(yx)

As described above, a typical TET system can be subdivided into twoparts, the transmitter and the receiver. Control and tuning may or maynot operate on the two parts independently. FIG. 4 is a schematicdiagram of a TET system having a wireless power transmitter 402 externalto a patient with a wireless power receiver 404 and medical device 406implanted within the patient. The transmitter 402 can be configured totransmit wireless power through the skin of the patient to the receiver404, which can provide energy to the medical device 406, or charge abattery connected to the device 406.

TET systems are highly sensitive and susceptible to interference, forexample, from other TET systems, metal objects, or objects with magneticsusceptibility. Accordingly, protections that can be implemented withina TET system to protect against adverse effects from these externalfactors. For example, the system can be configured to recognizesignificant influences and make adjustments accordingly. In anotherexample, the system can indicate to a user (e.g. a patient) the presenceof an undesirable factor so the user can take necessary precautionsand/or move away from the influencing factor. Additionally, the externalfactors can be handled differently depending on the state of theimplanted TET system. For example, how the system reacts to an externalfactor during wireless power transmission may be different than how thesystem reacts when there is not an external transmitter sending wirelesspower to the receiver implanted in the patient. In another embodiment,the system may react differently depending on the charge state of theimplanted battery.

In various embodiments, the system utilizes a troubleshooting algorithmsuch that, if the system performs unexpectedly, the algorithm can beimplemented to help a user, technician, and/or clinician determine ifthe cause is due to a fault in a system component, the presence of anunexpected external factor, and/or improper tuning and adjustment of thesystem. In one example in which the TET system is used in conjunctionwith a VAD, the clinician may notice during a regular visit that the VADis not providing sufficient circulatory support. The clinician thenneeds to determine if the pump is not working properly, if the powerneeds to be increased, or if the user has been around factors that arenegatively affecting the system (e.g. the patient's TET system isregularly exposed to a large number of ferromagnetic materials). Anexample of a troubleshooting algorithm for assisting a clinician withtroubleshooting an implantable medical device without requiring explantis described in U.S. Pub. No. US 2011/0313238 A1, incorporated hereinfor all purposes by reference.

The possible solutions involve, but are not limited to, (i) adjustingtuning to compensate for the external interference, (ii) turning off thetransmitter if powered by a battery and the energy losses are great,(iii) setting off an alarm to the patient to notify the patient of theexternal interference, (iv) a combination of (i) and (iii), or (v) acombination of (ii) and (iii). These solutions can be implemented withhardware and/or software on either the transmitter or the receiver orboth. In one embodiment, the TET system can set off an alarm and adjusttuning to compensate for the external factor. The patient alarm can bevisual, audible, vibratory, etc. The alarm can also be internal toanother component in the system, e.g., the alarm can be configured totrigger the transmitter to stop transmitting for a pre-set period oftime.

FIG. 5 illustrates a flowchart that explains the use of a protectivealgorithm by a TET system, such as the system shown in FIG. 4. Referringto step 502 of FIG. 5, first, the TET system can be classified as beingin one of two energy states. A “transmit state” can be when atransmitter of the TET system is transmitting wireless power to areceiver implanted in a patient. An “inactive state” can be when notransmission of power is occurring, e.g., the patient is not attemptingto transmit power from a transmitter to the receiver. It should beunderstood though, that in the scenario where a patient is in proximityto another transmitter (such as another patient's transmitter) thatinadvertent power transfer may occur without proper protections inplace.

Once the power state has determined, a TET system according to oneembodiment can include a system or method to detect the presence ofanother TET system or external interference. If the TET system is in an“inactive state”, then in step 504 of FIG. 5 the TET system candetermine if the receiver picks up any wireless power signals in thesame frequency band as the TET system operates in. Similarly, if the TETsystem is in a “transmit state”, transmission of wireless power from thetransmitter to the receiver can be halted at step 506, and then at step508 the TET system can determine if the receiver picks up any wirelesspower signals in the same frequency band as the TET system operates in.

If the TET system determines in either step 504 or step 508 that thereceiver is picking up interfering wireless power signals in the samefrequency band as the transmitter, the TET system can determine in steps510 and 512 that the TET system is in the presence of nearbyinterference, such as another TET system transmitting wireless powernearby. In some embodiments, the TET system can indicate to a user thatthere is a nearby interference. This indication can be in the form of anaudible indicator (e.g., a beep, alarm, etc). a visual indicator (e.g.,a light on the transmitter, a warning on a display of the transmitter,etc), or in the form of a message to the user or to a physician (e.g.,an email or text message alert).

In some embodiments, the TET system can be configured at step 506 totemporarily halt transmission of power at predetermined periods. Thefrequency of the “temporary halts” can be based on the receiver'sability to determine the frequency of an induced voltage, to ensure thatthe phase lock will not slip out of sync.

In embodiments where a separate transmitting TET system is detectednearby, at step 514 of FIG. 5 the transmitter of the TET system can becontrolled to phase match to the interference or other transmitter ofthe separate TET system to compensate for the interference. Note that ifthe separate TET system follows the same procedure, it will, during atemporary halt in its “transmit state”, detect the first TET system andcontinue the phase match.

In another embodiment when the TET system is in either an “inactivestate” or a “transmit state”, referring to step 516, one approach can beto check how much power the transmitter is receiving. If the TET systemis in the “transmit state”, the transmitter can determine how muchenergy is coming back to the transmitter from the receiver, and comparethis amount to calculated or tabulated values of how much power shouldbe expected under current operating conditions. If an excess amount ofenergy is coming back compared to the amount that is expected, this isan indicator that another transmitter is nearby and the system candetermine the presence of a nearby interference at step 520 of FIG. 5.Similarly, if the transmitter is in an “inactive state” and the receiveris still picking up some magnetic field, the TET system can use thisinformation to interpret the interfering external factor. Again, in boththese scenarios, the next step would be to match phase with the othertransmitter and/or indicate the interference to the user.

Whichever of the above algorithms is used, an alert can be provided tothe user to indicate that a foreign source has been detected and hasbeen phase matched. In one embodiment, the alert is upgraded to an alarmstatus if phase matching cannot be accomplished, because it means eitherthat some of the wireless power transmitted by the transmitter is beingsent to another system or that the receiver could be receiving netenergy. The former is undesirable, particularly if the transmitter isoperating off a battery source, as some energy is lost from the system.The latter is not bad in itself, but could become a concern if theforeign transmitter “gives away” more energy than the receiver canhandle.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

1-8. (canceled)
 9. A wireless power transfer system, comprising: atransmit resonator configured to transmit wireless power; a receiveresonator configured to be implanted in a human patient, the receiveresonator further configured to receive wireless power from the transmitresonator; and a controller coupled to the transmit resonator andconfigured to: determine the presence of interference that is capable ofaffecting transmission of wireless power from the transmit resonator tothe receive resonator; generate an alert to notify a user of theinterference; and control the wireless power transfer system to addressthe interference.
 10. The wireless power transfer system according toclaim 9, wherein to generate an alert, the controller is configured togenerate at least one of an audible indicator and a visual indicator.11. The wireless power transfer system according to claim 9, wherein togenerate an alert, the controller is configured to transmit at least oneof an email and a text message.
 12. The wireless power transfer systemaccording to claim 9, wherein to control the wireless power transfersystem, the controller is configured to tune at least one of thetransmit resonator and the receive resonator to compensate for theinterference.
 13. The wireless power transfer system according to claim9, wherein to control the wireless power transfer system, the controlleris configured to deactivate the transmit resonator.
 14. The wirelesspower transfer system according to claim 9, wherein to determine thepresence of interference, the controller is configured to determine thatthe receive resonator picks up a wireless power signal when the transmitresonator is deactivated.
 15. The wireless power transfer systemaccording to claim 9, wherein to determine the presence of interference,the controller is configured to determine an amount of power received bythe transmit resonator; compare the amount of power received to anexpected value; and determine the presence of interference based on thecomparison.
 16. The wireless power transfer system according to claim 9,wherein the interference is an additional transmit resonator.
 17. Amethod of operating a wireless power transfer system including atransmit resonator and a receive resonator, said method comprising:determining the presence of interference that is capable of affectingtransmission of wireless power from the transmit resonator to thereceive resonator; generating an alert to notify a user of theinterference; and controlling the wireless power transfer system toaddress the interference.
 18. The method of claim 17, wherein generatingan alert comprises generating at least one of an audible indicator and avisual indicator.
 19. The method of claim 17, wherein generating analert comprises transmitting at least one of an email and a textmessage.
 20. The method of claim 17, wherein controlling the wirelesspower transfer system comprises tuning at least one of the transmitresonator and the receive resonator to compensate for the interference.21. The method of claim 17, wherein controlling the wireless powertransfer system comprises deactivating the transmit resonator.
 22. Themethod of claim 17, wherein determining the presence of interferencecomprises determining that the receive resonator picks up a wirelesspower signal when the transmit resonator is deactivated.
 23. The methodof claim 17, wherein determining the presence of interference comprises:determining an amount of power received by the transmit resonator;comparing the amount of power received to an expected value; anddetermining the presence of interference based on the comparison. 24.The method of claim 17 further comprising transmitting wireless powerfrom the transmit resonator to the receive resonator.